Obesity is a risk factor for diabetes, cardiovascular disease events, cancer and overall mortality. Weight loss may protect against these conditions, but robust evidence for this has been lacking.

The findings from the majority of large and long-term epidemiological studies indicate that being overweight or obese is associated with increased mortality; the lifespan of severely obese individuals is decreased by an estimated 5 to 20 years depending on gender, age and race. Weight loss is known to be associated with an improvement in the intermediate risk factors for disease, suggesting that weight loss would also reduce mortality. However, with the exception of the Swedish Obese Subjects (SOS) trial, controlled intervention studies demonstrating that weight loss in fact reduces mortality have been lacking. To date, most observational epidemiological studies have indicated that overall and cardiovascular disease mortality are increased after weight loss, even in subjects who were overweight or obese at baseline. This discrepancy concerning the effects of weight loss on risk factors as compared to mortality has been related to certain limitations inherent to observational studies, particularly the inability of such studies to distinguish between intentional and unintentional weight loss. Thus, the observed weight loss might be the consequence of conditions that lead to death rather than the cause of increased mortality.

Lifestyle interventions to prevent diabetes have not prevented cardiovascular disease events after 10– 20 years of follow-up. Similarly, lifestyle interventions combined with antiobesity medication have either shown no effect on primary cardiovascular disease endpoints [28] or an increased incidence in the drug-treated group. Taken together, trials of nonsurgical weight loss .